Mechanisms of the composite face effect (CFE): Perceptual learning fails to reveal the effect in prototype-based artificial stimuli

This study investigated the role of perceptual learning in the composite face effect (CFE), which is characterized by reduced accuracy in recognizing the top half of a face when it is combined with the bottom half of another face, particularly when the composite is upright and aligned, compared to when the two halves are laterally offset (misaligned). The misalignment disrupts configural/holistic processing, affecting recognition performance. Experiment 1a (<i>n</i> = 96) employed prototype-defined checkerboards to investigate the presence of the composite effect. The advantage of using these stimuli is that expertise can be precisely controlled. Experiment 1b (<i>n</i> = 96) aimed to replicate the composite effect using face stimuli, serving as a control and enabling direct comparison of the effect between face and checkerboard stimuli. Both experiments employed a full design that included congruent and incongruent, aligned and misaligned composites to measure the composite effect. Results from Experiment 1a indicated that the composite effect could not be obtained with checkerboard composites, whereas Experiment 1b confirmed the robust presence of the CFE in face stimuli. Based on these findings, we can interpret that perceptual learning does not significantly contribute to the CFE.